1. The Field of the Invention
The present invention broadly relates to corrosion inhibited antifreeze compositions which are especially useful as coolants in heat exchange systems. In some of its more specific variants, the invention is concerned with a novel antifreeze composition and with a process employing the same to reduce the rate of corrosion of solder alloys used in automotive cooling systems.
2. The Prior Art
The concentrated prior art antifreeze compositions adapted to be diluted with water and used as coolants for internal combustion engines usually contain a major amount of a liquid water soluble alcohol as a freezing point depressant, about 0.5-5% by weight of additives, and the balance water. The freezing point depressant is usually ethylene glycol, but other water soluble alcohols are used to some extent. The additives may include one or more prior art corrosion inhibitors, an antifoam agent and/or a water pump lubricant. Often a combination of corrosion inhibitors provides greater protection against corrosion as the cooling system of a typical internal combustion engine contains a substantial number of different metals in contact with the circulating coolant.
A WIDE VARIETY OF INHIBITORS HAVE BEEN PROPOSED HERETOFORE FOR USE IN ANTIFREEZE COMPOSITIONS. Several examples of the prior art inhibitors include inorganic compounds such as metal phosphates, borates, molybdates, arsenates, arsenites, nitrates, nitrites and chromates, and various organic compounds such as mercaptobenzothiazole, benzotriazole, piperazine, propynyloxynitrobenzene, bis-(nitrohydroxyphenyl)-pentanoic acid, and certain carboxylic acids which differ markedly from the inhibitor disclosed herein.
The corrosion inhibitors available heretofore, have not been entirely satisfactory in all respects. For example, the prior art corrosion inhibitors do not aid in solubilizing the antifoam agents commonly used in antifreeze compositions and in a number of instances may even render it more difficult to dissolve a sufficient amount to be effective for the intended purpose. This is especially true of inhibitors added for the purpose of reducing the rate of corrosion of solder alloys which are used extensively in automotive cooling systems. As a result, the prior art antifreeze compositions often were deficient in their antifoam properties and/or they lacked outstanding inhibition properties in respect to reducing the corrosion rate of solder. These two properties are very important and both should be present to a maximum degree in an ideal antifreeze composition. However, such an antifreeze composition was not available prior to the present invention.